I am also reading Greg Bahnsen's book "Always Ready" (Greg being a [now deceased] presuppositionalist Sye knew and clearly admires).
What's interesting, reading this other stuff, is that while Sye clearly uses a lot of standard presuppositional stuff, some of his moves are novel. Here is an illustration:
Sye asks "What's your account of logic, etc.?"
Me "You mean, what makes the laws of logic hold? Well, I 'm not sure. But here are three answers I quite like." [I present them - one is Quinean and one Wittgensteinian. At least two explain why the laws of logic may not even require an "explanation" or "underpinning".)
Sye "But what's your account! You must have one! I am not going to deal with positions you don't even hold."
Me "But I am not committed to one."
Sye "Ah! So your world view cannot account for logic!"
Me "No. It may be one of these answers is correct. Or perhaps some other non-Christian view is. I am just not sure, that's all. But you say you have an argument that no non-Christian account can possibly be correct. What is it?"
Sye: "But what's your account of logic?"
And round and round we go. These moves are pure Sye, I think - all his own handiwork.
By the way, my own version of presuppositionalism is available here. It's fun using some of Sye's own "moves" against him.
Incidentally, there is one move open to presuppositionalists that Witmer does not deal with, which we might discuss. As Witmer says, it's open to an atheist to say, "Hey the laws of logic, moral principles, etc are just "brute" - they are basic features of reality not further explicable. They constitute our presuppositions. As we atheists are allowed to have presuppositions too, what's the problem with our world view? Where is the internal contradiction?"
I did point this out to Sye fairly early on, in fact (back in July/August).
Anyway, a presuppositionalist could reply:
"But what about simplicity? The God hypothesis is highly economical - on my world view, one single, simple thing accounts for logic, morality etc. etc. But on your world view, you need a whole load of different presuppositions to account for these different things. As your world view values simplicity, so it does at least contain an internal tension (you favour simplicity, yet your world view ends up being complex, requiring also sorts of things to be presupposed, rather than just one thing) - your own commitment to simplicity gives you reason to favour my world view over your own!"
I have my own ideas about how to deal with this move, but put it up for debate....